1. Field of the Invention
The disclosed technology generally relates to the field of digital receiver front-ends and of digital receivers including such a front-end.
2. Description of the Related Technology
Software-defined radio (SDR) is a collection of hardware and software technologies that enable reconfigurable system architectures for wireless networks and user terminals. SDR provides an efficient and comparatively inexpensive solution to the problem of building multi-mode, multi-band, multi-functional wireless devices that can be adapted, updated or enhanced by using software upgrades. As such, SDR can be considered an enabling technology that is applicable across a wide range of areas within the wireless community.
A software-defined radio platform can be seen as a step towards a cognitive radio system, a fully reconfigurable wireless black box that automatically changes its communication variables in response to network and user demands. Cognitive radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently avoiding interference with licensed or unlicensed users. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum, user behavior and network state.
Handheld digital receiver cost reduction and time-to-market improvement call for software defined radio (SDR) implementation. To be viable in portable handheld devices, SDR must also be low power. A variety of constraints results from this requirement. To meet the stringent specifications algorithm/architecture co-design is crucial for emerging radio systems like SDR.
A number of promising application scenarios additionally determine performance requirements. Wireless LAN (WLAN) to cellular handover is an appealing application scenario for SDRs, since it would allow seamless and opportunistic roaming between both types of networks, in order to obtain a predetermined performance in terms of power consumption and flexibility. Huge benefits in terms of performance and energy consumption are typically expected, but a main driver is of course the price per bit that could be significantly reduced. To support the handover decision, extra information about the current and target network is needed. The IEEE 802.21 standard supports cooperative use of information at the mobile node and within the network infrastructure. This means that both the mobile node and the network can make decisions about connectivity based on measurement reports supplied by the link layer. These measurement reports can be signal qualities, network loads or packet error rates. Hence, there is a need for a digital front-end circuit able to provide some basic measurement reports, e.g. signal qualities, for e.g. WLAN and long term evolution (LTE). In addition it should be able to perform a coarse time synchronization for both standards.
In the prior art solutions for synchronization are found wherein dedicated (hard-wired) synchronization blocks are applied. Coarse grain array-type synchronization blocks are known to be not very power efficient.
Regarding sensing most of the existing experimental platforms and measurements have been based either on expensive laboratory equipment, such as vector spectrum analyzers, with high sensitivity or very low-cost narrowband, limited sensitivity off-the-shelf demonstrators. Most of the existing sensing engine implementations have followed the FCC and focused specifically on the detection of TV-signals (good examples were early FCC demonstrator systems, e.g. from Microsoft and Philips, and work by several IEEE802.22 based projects). A sensing engine, with embedded feature detection algorithms, is currently unavailable in the civilian domain. The current state-of-the-art in spectrum sensing does not address practical concerns of building scalable, reliable, low-power sensing engines that fulfill stringent requirements.
Various platforms (TI, Intel platforms, . . . ) are known that combine accelerators with processors. The control is centralized by the processor and thereby does not allow asynchronous operation between the different processes (accelerator and processor core).
For emerging standards there is a need to scale up the overall architecture to 4G requirements and need to increase both the performance and the level of programmability of the current synchronization ASIP. This includes supporting bandwidths up to 100 MHz and improved MIMO operation.
For future radio architectures: need for flexible resampling & programmable filtering. An interpolator-based approach is envisaged, leading to very flexible rate-support.
For cognitive radio sensing and multi-band reception capabilities are required which have a significant impact on the architecture: without sensing, no cognitive radio. A desired solution should enable a) sensing power in specific subbands and b) selecting a specific band, down-convert to baseband and resample. In order to allow multi-band reception, multiple ‘paths’ are required.
From patent application WO2007/132016 a digital receiver structure is known that enables environment awareness and gradual system wake-up in response to incoming radio transmission.
The paper “A cognitive radio approach to realize coexistence optimized wireless automation systems” (K. Ahmad et al., IEEE Conference on Emerging Technologies & Factory Automation, 22 Sep. 2009, pp. 1-8) is basically concerned with coexistence of multiple radio systems. The use of software defined radio is proposed to allow multi-mode, multi-band and multi-functional wireless radios that can be modified by software upgrades. A set-up with a master transceiver and slave transceiver is used. The described flow is completely in software. Demodulation and sensing are performed in parallel in the receive path, but the paper is not at all concerned with the power efficiency of the proposed architecture. A receive platform is shown with in parallel a spectrum analyzer. When power is detected in the 2.4 GHz band, the transmitter is switched to another band.